1. Field of the Invention
The present invention relates to a lens barrel for a camera having a built-in ultrasonic motor that drives a photographing or shooting lens.
2. Related Background Art
A lens barrel having a built-in ultrasonic motor in which a stationary member as a vibration generating member of the ultrasonic motor and a manual operation member are connected so that the stationary member and the manual operation member rotate with respect to a fixed portion of the lens barrel, and in which the lens operating mode is selected by actuating an electrical switch, is known.
In such a lens barrel, when a manual focus adjustment mode is selected using a mode selection member, i.e., by actuating the electrical switch, a relative moving member or rotor and the stationary member of the ultrasonic motor become united and rotate as a single body in conjunction with the manual operation member (e.g., a manual operation ring that is rotated by a photographer) to drive a photographing optical system.
When an automatic focus adjustment mode is selected, the stationary member is fixed and does not rotate with respect to the fixed barrel. The stationary member of the ultrasonic motor vibrates to impart rotational movement to other components of the lens barrel, and the photographing optical system is driven by rotation of the moving member caused by vibration of the stationary member.
Consequently, when the manual focus adjustment mode is selected, the photographing optical system can be driven without damaging the surfaces of the stationary member and the relative moving member of the ultrasonic motor that contact each other.
FIG. 3 is a cross-sectional view that illustrates a conventional lens barrel 2 having a built-in ultrasonic motor (see, e.g., Laid-Open Japanese Patent Application No. Hei 4-343310).
FIG. 4 is a cross-sectional view that illustrates a power supplying section of the lens barrel shown in FIG. 3. FIG. 5 is a schematic block diagram that illustrates a power supply circuit of the lens barrel of the prior art.
FIG. 3 illustrates the lens barrel in the automatic focus adjustment state in which a focus adjustment optical system L2 and L3 is driven by the rotation of an ultrasonic motor Mo (FIG. 4), and a mode selection switch 20 is set to the automatic focus adjustment mode.
The focus adjustment optical system L2 and L3 is supported by a lens holding barrel 2 and effects focus adjustment by moving in the direction of the optical axis. The lens holding barrel 2 is fitted movably in the direction of the optical axis in an inner periphery of a center intermediate diameter portion la of a fixed barrel 1. A pin 3 is provided on the outer periphery of the lens holding barrel 2 . The pin 3 protrudes through a guide groove provided in the center intermediate diameter portion 1a in parallel with the optical axis. The tip of the pin 3 engages a cam groove 4a provided on the inner peripheral surface of a cam ring 4. The cam grooves 4a is so formed to move the lens holding barrel 2 in the direction of the optical axis by engagement of the cam groove 4a with the pin 3 when the cam ring 4 is rotated in the manner described hereinafter.
A pin 5 protrudes from the outer periphery of the center intermediate diameter portion 1a of the fixed barrel to engage a circumferential groove 4b provided on the inner peripheral surface of the cam ring 4. Consequently, the cam ring 4 cannot move in the direction of the optical axis and thus can only rotate by a predetermined angle about the optical axis. The cam ring 4 also includes a distance scale that is displayed on the right side large diameter outer peripheral portion 4c of the cam ring 4.
A stator or stationary ring member 6 of the ultrasonic motor Mo is fitted on the outer periphery of a center small diameter portion 1c of the fixed barrel 1 to rotate freely about the optical axis.
A biasing member 11 is provided between the center small diameter portion 1c of the fixed barrel 1 and the stator 6 and urges the stator 6 to an inner side surface of the large diameter portion 1d of the fixed barrel 1 through a glass epoxy plate 15, thereby imparting a predetermined friction torque so that the stator 6 may not rotate easily when the automatic focus control mode is selected.
A window member 8, which is formed of a transparent synthetic resin, is disposed on the large diameter unit 1d of the fixed barrel 1. The window member 8 displays the distance scale on the outer periphery 4c through an intermediate ring 7. The intermediate ring 7, which is preferably formed of transparent synthetic resin, is fitted on the inner surface of a manual operation ring 10 rotatably therewith.
A rotor or rotating member 9 (i.e., the relative moving member of the ultrasonic motor Mo) is so disposed to frictionally contact the stator or stationary member 6 at their radially extended surfaces each other and to be rotatable about the optical axis through a bearing 12a relation to the stationary member 6. In particular, a biasing member 14 causes the stationary member 6 and the rotating member 9 to contact at their radially extended surfaces each other via an annular plate 13 and a bearing 12b. An engagement groove 9a is provided on the left side of the rotating member 9 to engage an engagement protrusion 4d on the right side of the inner periphery of the large diameter portion of the cam ring 4. Consequently, the rotating member 9 and the cam ring 4 rotate together.
The manual operation ring 10 is fitted on both the large diameter portion 1d of the fixed barrel 1 and the left side large diameter portion 1e. The manual operation ring 10 cannot move in the direction of the optical axis, but it can rotate freely about the optical axis.
A glass epoxy plate 15 is fixed to the stationary member 6 and includes ring-shaped conductive portions 15a that extend around the entire circumference , as shown in FIG. 4. The glass epoxy plate 15 is formed with through-holes 15b at positions offset from the ring-shaped portion through which the conductive portions 15a form an electrical connection with the stationary member 6 at the rear surface of the glass epoxy plate 15. A brush 16 contacts the top surface of the conductive portions 15a, establishing an electrical connection with the stationary member 6 regardless of its angular position.
A pressure plate 17 urges the brush 16 toward a fixed brush plate 18 to fix the brush thereonto . The fixed brush plate 18 is attached to the fixed barrel 1 by small screws 19.
The mode selection switch 20 slides in the direction of the optical axis on the fixed barrel between the manual focus adjustment mode position M and the automatic adjustment mode position A. The mode selection switch is configured to generate an electrical signal in accordance with either mode when the switch is activated.
A switching plate 21 is attached to the mode selection switch 20 by a small screw 23. A plate spring 22 is attached to the fixed barrel 1 by a small screw 24. The plate spring 22 is disposed to cooperate with a plurality of engagement grooves 6a that are provided on the outer periphery of the stationary member 6.
When the mode selection switch 20 is slid to the M position, i.e., when the manual focus adjustment mode is selected, the switching plate 21 moves simultaneously, thereby pushing up the plate spring 22 radially outwardly as indicated by the dotted line in FIG. 3. As a result, the plate spring 22 is withdrawn from the engagement grooves 6a. When the engagement grooves 6a of the stationary member 6 are separated from the plate spring 22, the manual operation ring 10 can be rotated.
When the mode selection switch 20 is slid to the A position, i.e., when the automatic focus adjustment mode is selected, the switching plate 21 is moved simultaneously, thereby allowing the plate spring 22 to return to its initial position as indicated by the solid line in FIG. 3. As a result, the plate spring 22 engages the engagement grooves 6a of the stationary member 6, and the manual operation ring 10 stops rotating.
The lens barrel is designed to satisfy a condition C&lt;B&lt;A, where A is friction torque between the stationary member 6 and the rotating member 9, B is friction torque between the fixed barrel 1 and the stationary member 6, and C is torque necessary to drive the lens holding barrel 2.
&lt;Automatic Focus Adjustment Mode&gt;
In operation, when the automatic focus adjustment mode is selected, the engagement grooves 6a of the stationary member 6 are engaged with the plate spring 22. Consequently, the manual operation ring 10 and the stationary member 6 stop rotating.
When a power source is connected to the ultrasonic motor Mo by a control mechanism (e.g., such as a power source unit 100 as shown in FIG. 4), ultrasonic waves are generated in the stationary member 6, and the rotating member 9 rotates in the circumferential direction. When the rotating member 9 rotates, the rotating member 9 and the cam ring 4 rotate together because the engagement groove 9a on the right side of the rotating member 9 engages the engagement protrusion 4d on the cam ring 4. When the cam ring 4 rotates, the lens holding barrel 2 moves along the optical axis so that automatic focus adjustment is conducted.
&lt;Manual Focus Adjustment Mode&gt;
In the manual focus adjustment mode, the mode selection switch 20 is in the position M, and power is not supplied to the ultrasonic motor Mo. When the mode selection switch 20 is slid to the M position, the plate spring 22 is depressed radially outwardly and becomes separated from the engagement grooves 6a. When the engagement grooves 6a and the plate spring 22 are separated from each other, the manual operation ring 10 can rotate. Power is not supplied to the ultrasonic motor Mo in this case, so the ultrasonic motor Mo does not drive the lens barrel. The stationary member 6 and the rotating member 9 are firmly pressed together by the biasing member 14.
Because the friction torque A between the stationary member 6 and the rotating member 9 and the torque C necessary for driving the lens holding barrel 2 satisfy the condition C&lt;A, the stationary member 6 and the rotating member 9 rotate together with the intermediate ring 7 when the manual operation ring 10 rotates.
The rotating member 9 and the cam ring 4 rotate together because the engagement groove 9a on the left side of the rotating member 9 and the engagement protrusion 4d of the cam ring 4 are engaged. When the cam ring 4 rotates, the lens holding barrel 2 is moved in the direction of the optical axis, and manual focus adjustment is conducted.
As described above, when the automatic focus adjustment mode is selected, the mode selection switch is in the A position, and the engagement grooves 6a are engaged with the plate spring 22, whereby the manual operation ring 10 and the stationary member 6 stop rotating.
The friction torque B between the fixed barrel 1 and the stationary member 6 and the torque C necessary for driving the lens holding barrel 2 satisfy the condition C&lt;B, even when the engagement grooves 6a and the plate spring 22 are not engaged . Therefore, when there is no engagement between the grooves 6a and the plate spring 22, only the rotating member 9 rotates (i.e., the stationary member 6 does not rotate). In other words, which focus adjustment mode has been selected can be ascertained by determining whether power is supplied to the ultrasonic motor Mo.
Accordingly, it becomes very easy to adopt a mechanism for effecting speedy change-over of such functions or modes as "go-home" photographing function in which an arbitrary photographing distance has been previously stored in memory and after a photographing is effected at a different photographing distance the lens is driven to the stored photographing distance, as well as a manual focus adjustment mode priority function in which, during phototaking in the automatic focus adjustment mode, the manual operation ring is rotated to thereby change over to the manual focus adjustment mode, since mechanical change-over becomes unnecessary.
The output torque from the moving member and the number of rotations in the ultrasonic motor described above are determined primarily according the size and shape of the motor. In other words, when the torque required to move the photographing optical system is determined, the number of rotations is known. Accordingly, when the time necessary for the photographing optical system to move from a photographing distance of infinity (.infin.) to a close position is determined the corresponding angle through which the moving member must be rotated is also known.
With the conventional lens barrel described above, however, when the manual focus adjustment mode has been selected, the rotor or moving member (i.e., the relative moving member ) and the stationary member or stator of the ultrasonic motor rotate together to drive the photographing optical system by the rotation of these components in conjunction with the manual operation of the manual operation member. Consequently, the angle necessary for rotating the manual operation member from a photographing distance of infinity (.infin.) to a close position is determined. A problem arises, however, when the angle is too small to allow manual focus adjustment.
The applicant has proposed a lens barrel with a built-in ultrasonic motor which overcomes the abovementioned problem in Laid-Open Japanese Patent Application No. 8-114739 (which corresponds to U.S. patent application Ser. No. 08/539,434 now U.S. Pat. No. 5,708,872).
FIG. 6 is a cross-section showing an embodiment of the lens barrel with the built-in ultrasonic motor proposed in JP8-114739.
In this embodiment, there are provided a plurality of rollers 25 each supported on a rotary shaft 26 whose center line is perpendicular to the optical axis and which in turn is provided on the outer periphery of the stationary member 6. Each roller 25 is in frictional contact with the fixed barrel 1 and the intermediate ring 7. Accordingly, if the manual operation ring 10 is rotated, the stationary member 6 is rotated about the optical axis on the outer periphery of the center small diameter portion 1c of the fixed barrel 1 through the intermediate ring 7 and the rollers 35.
The angle of rotation of the stationary member 6 at this time is a half of the angle of rotation of the manual operation ring 10 according to the principle of a planetary gear device.
This means that an angle required for rotating the manual operation ring from an infinite (.infin.) photographing distance to a close distance becomes larger than the angle of rotation of the rotor or moving member of the ultrasonic motor, thereby fine manual adjustment becoming possible.
As described, the lens barrel with the built-in ultrasonic motor proposed in JP8-114739 can overcome effectively the problem of the prior art.
In the proposed lens barrel, however, the ratio of the angle of rotation between the manual operation member and the stationary member is fixed to 2:1.
However, with respect to the angle of rotation of the manual operation member from an infinite (.infin.) photographing distance to a close photographing distance, a range in which good focusing operability can be obtained, depends on the specification of the lens barrel, such as, on the focusing length, close distance value and the like.
For this reason, the proposal made in JP8-114739 can not provide a lens barrel having good operability on manual focusing adjustment for all the specifications.